The vast majority of electrocardiological testing is performed in a cardiologist's office or the hospital. In either case, a quality electrocardiograph printout generally comprises twelve separate tracings obtained from a predetermined combination of signals from a plurality of electrodes. Trained personnel are required to properly position the electrodes on the patient, and an electrode gel is applied to the skin of the patient to enhance signal clarity. Signals are processed and filtered by conventional electrocardiograph (ECG) equipment, and the graphic output or printout from the ECG equipment may be used by the cardiologist to evaluate and diagnose coronary disorders or establish baseline cardiac data.
The above procedure is both expensive and time consuming, especially when a coronary out-patient must make regular weekly visits to the cardiologist to evaluate coronary recovery or monitor baseline data. Because of the limited mobility of some patients, doctors frequently keep a patient in the hospital for an extended period to perform regular ECG testing.
It has been known for some time that a tremendous time and cost savings could be realized if the untrained patient could generate ECG data without professional assistance. Also, additional savings could be realized if the patient could generate such data at his home or office, and transmit or forward the data to the ECG evaluation equipment at the cardiologist's office or at the hospital. The problem, however, has been that prior art methods and apparatus are not clinically and professionally acceptable to the cardiologist and/or fail to gain patient confidence and approval. Thus, such prior art methods and apparatus have not been widely used and accepted to date.
Prior art garments typically utilize an elastic cloth front portion specifically tailored to the individual patient. U.S. Pat. No. 2,685,881 teaches a rubber strap for holding a single electrode. Single electrodes, however, are simply not capable of generating a desired complete ECG printout necessary for the cardiologist. U.S. Pat. No. 3,409,007 teaches a vest-like garment fabricated from elastic cloth, with the desired plurality of electrodes. The front portion of the panel preferably has a substantial measure of elasticity in at least two orthogonal dimensions, and band-like appendages are provided for the limb electrodes. U.S. Pat. No. 3,534,727 teaches a garment with flexible elastic electrodes, with the electrodes held in contact with the patient's body by the skin tight garment. U.S. Pat. No. 3,525,330 describes an elastic cloth garment with a grid-like pattern for prescribing the location of electrodes. U.S. Pat. Nos. 4,121,575 and 4,202,344 teach an expandable or stretchable non-conductive strip, such as rubber sheeting, for the six precordial electrodes, while the limb lead electrodes may be of the conventional type. As stated for example in U.S. Pat. No. 4,202,344, the front garment material is stretchable so that when the garment is worn by the patient, the electrodes automatically assume the correct anatomic location on the chest, and thus the position of an electrode moves relative to another electrode depending on the degree the support material is stretched. U.S. Pat. No. 3,409,007 indicates that a portion of the front panel may be provided with multiple thickness of elastic cloth to provide "additional resilient stiffness" to that portion of the garment.
Prior art electrodes are frequently of the "wet" type, wherein a gel is used to increase the clarity of the signal from the electrodes. Many types of electrodes have been described in the prior art, but they generally suffer from poor signal clarity or require a gel to increase signal clarity. U.S. Pat. Nos. 2,685,881 and 3,144,018 each depict a crude metal electrode, while U.S. Pat. No. 3,534,727 illustrates a "flexible" electrode. U.S. Pat. No. 4,121,575 describes a hollow construction electrode which permits the introduction of an electrolyte paste or gel, and U.S. Pat. No. 4,202,344 teaches various bell or cup-shaped electrodes, which also may have a passageway for an electrolyte paste or gel, and which may be held against the body of the patient by the stretch of the chestpiece.
Telephonic units for transmitting ECG signals to ECG receiving equipment at the cardiologist's office are described generally in U.S. Pat. No. 3,910,260. More specific apparatus is described in U.S. Pat. No. 3,426,150, which includes a known value modulation signal for calibration of instruments, and a muting circuit to permit speech transmission over the unit. An exercise measuring system and related electronic apparatus are depicted in U.S. Pat. No. 3,802,698, and a portable cardiac monitoring system and method is described in U.S. Pat. No. 3,991,747. Finally, U.S. Pat. Nos. 3,029,808, 3,199,508, and 3,717,141 each depict electrical apparatus and systems for obtaining signals from skin locations on an individual.
These prior art methods and apparatus are difficult to utilize by an untrained patient, do not result in highly reliable and repeatable ECG signals, and do not satisfy the requirements of many cardiologists and patients. The disadvantages of the prior art are overcome by the present invention, however, and improved methods and apparatus are hereinafter provided for obtaining and transmitting ECG data to conventional graphic output equipment.